[lld] [lld][AArch64][ELF][PAC] Support AUTH relocations and AUTH ELF marking (PR #72714)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Do we really need to support .note.AARCH64-PAUTH-ABI-tag `NT_ARM_TYPE_PAUTH_ABI_TAG`?
GNU program properties are well-integrated in glibc now.
If they choose to implement the pauth ABI, and toolchains support program properties, it's likely they'll leverage this established system, avoiding .note.AARCH64-PAUTH-ABI-tag.
Since there is no counterpart for GNU_PROPERTY_AARCH64_FEATURE_1_BTI and PAC in .note.AARCH64-PAUTH-ABI-tag, it seems even less motivation for .note.AARCH64-PAUTH-ABI-tag, since an extra note section would just increase code size.

FreeBSD, with its existing return address pauth support, also seems content with GNU program properties.

https://github.com/access-softek/musl/tree/dkovalev/pauth-code-drop may need an update


https://github.com/llvm/llvm-project/pull/72714